"Can you describe what that "packing matrix" would look like? What makes up the rows? The columns?
This sounds like a "cross tab report" and such is possible to set up in FileMaker, but it takes a bit of design work to get it up an running.
Does the data really need to be arranged in a matrix?
If you arrange the data in more of an "invoice" or "packing list" format with a heading that identifies the site followed by a list of items and quantities, it's much less work to set up.
I guess the easiest way to describe it is, addresses down the side, printed items along the top. Each cell corresponding to that printed item for that address would contain the quantity to be delivered anything from 0 - 1000.
We have always used a spreadsheet/matrix format historically. I guess an individual packing list for each site would be OK, but not perfect.